The present invention relates to a process for preparing a molded article of a hydrolyzed ethylene-vinyl acetate copolymer (hereinafter referred to as "EVOH"), and more particularly to a process for preparing EVOH molded articles having a good gas-impermeability and superior in flex-crack resistance, stretchability and thermoformability.
EVOH has an excellent gas-impermeability. When EVOH molded in the form of film or sheet is subjected to thermoforming, e.g. vacuum forming, a good thermoformability and a sufficient elongation or stretchability are required. In case of imparting flex-crack resistance, stretchability and thermoformability to EVOH molded articles, there has hitherto been adopted a method wherein EVOH is blended with a polyolefin.
However, for providing EVOH molded articles with a flex-crack resistance satisfactory for practical use, it is necessary to blend EVOH with a large quantity of a polyolefin. Generally the melting point of EVOH is higher than that of a polyolefin. Therefore, in case that a large amount of a polyolefin is added to EVOH at once and the blend is molded, the polyolefin which has a lower melting point melts prior to EVOH, so matrix formation of EVOH is made unstable, thus resulting in deterioration of gas-impermeability.
Recently, in order to solve the above problem encountered in blending EVOH with a polyolefin, it is proposed to use an acid-modified polyolefin or the like as a compatibilizer. This proposal surely improves the gas-impermeability to some degree, but the improvement is only on a low level. Moreover, the obtained EVOH films or sheets are insufficient in flex-crack resistance and stretchability.
An object of the present invention is to provide a process for preparing a molded article of EVOH having an improved flex-crack resistance without deteriorating the gas-impermeability.
A further object of the present invention is to provide a film or sheet-like molded article of EVOH having an excellent gas-impermeability and having improved flex-crack resistance, enlongation or stretchability and thermoformability.
These and other objects of the present invention will become apparent from the description hereinafter.